Preparation and performance study of anti mud polycarboxylic acid slump retaining agent

Anti-mud polycarboxylic acid slump retaining agent was prepared by copolymerization of ethylene glycol monovinyl polyethylene glycol ether, diethyl 4-vinylphenyl phosphate, 2-methyl-2-(4-vinylphenyl) propionic acid, unsaturated carboxylic acid (or unsaturated carboxylic anhydride) and unsaturated carboxylic ester under the action of initiator and molecular weight regulator. The effect of the slump retaining agent on the workability of fine aggregate concrete with different mud contents was tested, and the sensitivity of the slump retaining agent to the mud content of machine-made sand was evaluated. At the same time, the viscosity reduction performance of the slump retaining agent was evaluated by using the emptying time of the inverted slump cone and the flow time of V-funnel and L-box. The experimental results show that the synthesized anti-mud polycarboxylic acid slump retaining agent has favourable effects of anti-mud and viscosity reduction.


Introduction
Polycarboxylic acid slump retaining agent was very environmentally friendly because of its good slump retaining property and high molecular designability, and it does not produce harmful substances such as ammonia and formaldehyde in the production process.In recent years, due to the increasingly severe situation of high-quality sand and gravel in our country, the supply of sand and gravel materials and natural sand materials in many areas has been in short supply, which leads to an extremely unstable supply of sand and gravel materials and high silt content in sand and gravel.Ordinary polycarboxylic acid slump retaining agents on the market can no longer meet the application performance of concrete.
In practical applications, an increase in the mud content of sand and gravel will significantly reduce the effectiveness of polycarboxylate slump stabilizers, leading to problems such as low water reduction rate and significant slump loss in concrete.Therefore, the composition and content of sand and gravel limit the application and popularization of polycarboxylic acid slump retaining agents [1][2][3][4][5][6] .In addition, in order to realize high-strength economical concrete, the water-binder ratio of concrete was usually reduced in engineering construction.However, in the preparation process of low waterbinder ratio concrete, the slurry viscosity was large and the construction was difficult, and the practical use of polycarboxylic acid slump retaining agent would cause adverse reactions such as segregation and bleeding in the later stage of concrete.Therefore, in the actual construction, it was necessary to control the concrete to maintain good viscosity to ensure its various properties [7] .So, we should continue to improve the molecular structure of the polycarboxylic acid slump retaining agent to make it have a high retention function, which was the future development direction of the polycarboxylic acid slump retaining agent field [8][9] .
The main difference between the EPEG six-carbon monomer and the existing HPEG monomer was the molecular structure characteristics of the EPEG monomer itself.EPEG-AA copolymerization was a non-ideal copolymerization reaction, and the distribution of macromonomer blocks in the graft copolymer formed in the reaction was more uniform and the molecular structure was more reasonable.The unsaturated double bonds in EPEG molecular structure are connected with oxygen atoms to form a group of C-O bond molecular structures.The change of molecular structure will shift the distribution of double bond electron cloud, thus changing the charge environment of unsaturated double bonds in EPEG polyether.The double bond in the EPEG molecule was a substitution structure, so the swing of the polyether side chain can be more flexible through the swing of the polyether side chain and the reduction of space resistance.With the increase of the swing freedom of the polyether side chain, the wrapping and winding of the polyether side chain were improved, so the synthesized polycarboxylic acid slump retaining agent has higher adaptability, and the effect was more obvious when the silt content of sand and gravel materials was high [10][11]

Test raw materials
Cement (C, YuXiu brand, P.O 42.5R); Machine-made sand: produced in Guangzhou, Huizhou, Heyuan, etc., with a fineness modulus of 2.7-3.0.Among them, Machine-made sand 1 has a mud content of 3.3%, Machine-made sand 2 has a mud content of 6.5%, Machine-made sand 3 has a mud content of 8.8%, Machine-made sand 4 has a mud content of 11.0%, and Machine-made sand 5 has a mud content of 13.6%; Water washed sand: Guangzhou, with a fineness modulus of 2.8; Stone: Foshan, continuously graded crushed stone with a particle size of 5 mm~20 mm; Fly ash (FA): Foshan, Grade II; Mineral powder (K): Foshan, S95 grade; Water: tap water that meets the requirements of national standards; Water reducing agent: commercially available conventional polycarboxylic acid slump reducer, WR-S; Self-made mud powder: the powdery material is obtained by taking Machine made sand 5 and passing it through a 0.08 mm standard sieve.

Synthesis Method of KZJ
180.00 g of EPEG, 1.0 g of 4-vinylphenyl phosphate diethyl ester, 1.5 g of 2-methyl-2-(4-vinylphenyl) propionic acid, 2.5 g of SHP, 0.005 g of green alum, and 145.0 g of water are added to a four-necked flask.The mixer and temperature control device are activated, and after the materials are well mixed, the addition of Components A, B and C is started dropwise.Among them, Component A consists of a mixture of 5 g AA, 2 g MAH, 28 g HPA, and 20 g water, Component B consists of a mixture of 1.5 g H 2 0 2 and 20 g water, and Component C consists of a mixture of 0.4 g VC and 20 g water.The initial reaction temperature was 12~18℃, the dripping time was 1 hour, and the material temperature was controlled to be below 25℃ during the dripping process.After the dripping was completed, the copolymer product was prepared by holding it for 1 hour.An appropriate amount of NaOH was added to the prepared copolymer product, so that the pH value was between 5.0 and 7.0, to obtain the required anti mud polycarboxylic acid slump inhibitor, abbreviated as KZJ.

Performance test method
2.4.1.Fourier transformer infrared spectra (FTIR) measurement.FTIR was obtained from the pressed disc of APC and KBr.The spectra in the range of 4000-400 cm-1 were recorded on Perkin Elmer Spectrum 100 FTIR spectrophotometer.

Slurry fluidity test.
According to the standard method in GB/T8077-2012 "Test method for homogeneity of concrete admixtures", the water-cement ratio was 0.29.

Test concrete mix ratio
Table 1 shows the mix proportion used for concrete performance verification in this paper.

FTIR test
From Figure 1, it can be seen that at 1726 cm -1 , there was a stretching vibration absorption peak of the ester group (-C=O-); the characteristic absorption peaks of -CH-and -CH 2 -are 2870 cm -1 , 1455 cm -1 , and 1349 cm -1 , respectively; 1106 cm -1 was the characteristic absorption peak of polyether long chain C-O-C-, and the functional groups of KZJ and WR-S were basically the same.The difference between KZJ samples was that there was a characteristic peak at 1644 cm -1 , indicating that KZJ formed a branched chain structure containing carboxylic acid groups during the reaction process, which was consistent with the designed structure.

Effect of Polycarboxylic Acid Slump Retaining Agent on the Flowability of Clean Slurries with Different Mud Content
The dosage of polycarboxylic acid slump retention agent was 0.25%, and some cement was replaced by an equal amount of mud powder.The influence of KZJ and WR-S on the fluidity of cement paste under different mud powder contents was tested, and the results are shown in Table 2. From Table 2, it can be seen that under different mud powder contents, KZJ has a higher initial fluidity and less loss over time compared to WR-S.Especially when the mud powder content is around 5%, after adding WR-S, the net slurry is completely immobile after about 1 hour, but when adding KZJ, the net slurry fluidity is 190 mm after 1 hour.From this, it can be seen that the anti mud effect of KZJ is significantly better than WR-S.

Influence of Mud Content and Polycarboxylic Acid Slump Retaining Agent on the Slump of Concrete
The C30 mix ratio is used to mix concrete, and the initial slump of the concrete is controlled to be (210±10) mm.The influence of mud content and polycarboxylic acid slump retention agent on the slump of the concrete is shown in Table 3.When the mud content of machine-made sand fluctuates around 3.3%, the influence of KZJ and WR-S on the fluidity of concrete is equivalent.But when the mud content of the machine-made sand is about 6.5%, the KZJ additive can significantly improve the slump retention of the concrete, with a slump loss of 15 mm and an expansion loss of 40 mm after 0.5 h.When using ordinary WR-S, the slump loss at 0.5 h is 30 mm, and the expansion loss is 90 mm.KZJ has a better anti mud effect on concrete with a mechanical sand content of 8.8% compared to WR-S.
When the mud content in machine-made sand is greater than 11% and KZJ was used, the concrete slump loss was 25 mm and the expansion loss was between 65 mm.When using ordinary WR-S, the slump loss was 50 mm and the expansion loss was as high as 200 mm.KZJ has a better anti mud effect on concrete with a mechanical sand content of 11% compared to WR-S.
The test results of comparing the fluidity of concrete and cement paste are basically consistent.However, due to the increase in mud content, even with the use of KZJ, the overall fluidity loss of concrete still gradually increases, and the strength of concrete also gradually decreases.Therefore, it was necessary to avoid using fine aggregate pre-mixed concrete with excessive mud content as much as possible to prevent damage to the mechanical properties and durability of concrete caused by mud content.

The Viscosity Reducing Performance of Synthetic Polycarboxylic Acid Slump Retaining Agent and Its Influence on the Compressive Strength of Concrete
Sand 1 is selected and a C60 mix ratio is used for pre-mixed concrete.The initial slump expansion of concrete is controlled at around 580 mm.Inverted slump cylinder emptying, V-shaped funnel and Lshaped box testing were conducted on KZJ and WR-S, and the results are shown in Table 4. From the above table, it can be seen that compared to WR-S C60 concrete, KZJ C60 concrete has a shorter initial inverted slump tube emptying time, V-shaped funnel flow time, and L-shaped box flow time.Therefore, KZJ can effectively reduce the initial viscosity of high-strength concrete.After 1 hour, the emptying time of the inverted slump cylinder, the flow time of the V-shaped funnel, and the flow time of the L-shaped box of KZJ C60 high-strength concrete are all smaller than those of WR-S C60 concrete.Therefore, KZJ has a more significant viscosity-reducing effect on the state of high-strength concrete after 1 hour of loss compared to WR-S.In addition, the compressive strength of KZJ C60 concrete at 7 and 28 days was higher than that of WR-S.

Conclusion
According to the principle of molecular design, free radical polymerization was used to prepare anti mud polycarboxylic acid slump stabilizers by introducing phosphate functional groups with strong calcium ion adsorption ability.The following conclusions have been drawn through research:  A new type of mud-resistant polycarboxylate slump inhibitor was prepared through a polymerization reaction between raw materials such as EPEG, AA, HEA, and methyl 4-vinyl benzoate.
 The infrared spectrum results indicate that EPEG undergoes polymerization reactions with various monomers, and the structure of the reaction products meets the expected requirements for various work in a wide temperature range. Through concrete performance tests with a different mud content of machine-made sand, it was found that the anti mud type polycarboxylic acid slump inhibitor has a good anti mud effect and good working performance in concrete with mud content higher than 6.5% of machine-made sand, and has broad application prospects. According to concrete-related fluidity tests, compared to WR-S, KZJ has a shorter emptying time, V-shaped funnel flow time, and L-shaped box flow time for slump cylinders, indicating that KZJ has a better viscosity reduction effect.

2. 4 . 3 .
Performance test.The working performance of concrete shall be carried out following GB/T 50080-2016 "Standard Test Methods for Performance of Ordinary Concrete Mixtures".Mechanical performance testing shall be carried out following GB/T50081-2002 "Standard Test Methods for Mechanical Properties of Ordinary Concrete".2.4.4.V-shaped funnel flow time test.The V-shaped funnel flow time test is in accordance with CECS 203-2006 "Technical Specification for Application of Self-compacting Concrete".The flow time test of L-shaped box shall be conducted in accordance with CCES 02-2004 "Guidelines for Design and Construction of Self-compacting Concrete".

Figure 1 .
Figure 1.Infrared Spectral Analysis of KZJ and WR-S.

Table 2 .
Fluidity Test of Cement Paste.mm

Table 4 .
Inverted Slump Cylinder Evacuation, V-shaped Funnel, and L-shaped Box Testing.